Increasing carbon dioxide concentration in the atmosphere is directly related to the present environmental problems such as global warming. Power plants that burn fossil fuel generate about 40% of the CO2 emissions worldwide. It is predicted that under a business-as-usual scenario (e.g., no CO2 emission mitigation), global CO2 emissions from coal combustion will increase from 9 Gton/year in 2000 to 32 Gton/year in 2050. Therefore, the control of CO2 emissions demands the development of new and better technologies. There different strategies are normally used to achieve CO2 separation and capture from a fossil-fired power production: post-combustion, pre-combustion and oxyfuel.
Membrane systems have the potential to separate carbon dioxide at lower costs and with lower energy penalties than other related technologies. High temperature CO2-permselective membranes could be applied to pre and post-combustion process for CO2 capture. Furthermore, high temperature CO2-permselective membranes could be used in reactions involving CO2, such as water gas shift reaction or provide other types of innovative process designs, such as integrated gasified combined cycle (IGCC). Similarly, many processes in chemical and refinery industries involve CO2 either as a reactant or product. One reaction is dry-reforming of methane with CO2 to produce hydrogen. High temperature CO2-permselective membranes can be used in membrane reactors to improve the efficiency of these chemical reaction processes.
Many early efforts have been reported on developments of microporous inorganic membranes for CO2 separation. These membranes are perm-selective for CO2 at low temperatures only. Dense, nonporous ceramic membranes are known for the infinitely large selectivity for O2 over N2 and other gases, and high O2 permeance at temperatures above 700° C. Research efforts on synthesis of dense Li2ZrO3 and Li4SiO4 membranes for high temperature separation of CO2 were reported, but these membranes exhibit a CO2/N2 selectivity of about 5 and CO2 permeance of 10−8 mol/s·Pa·m2 at 525° C. It is known that molten carbonate, such as Li2CO3/K2CO3, can conduct CO32− at a very high rate at high temperatures. A metal-carbonate dual-phase membrane was prepared and shown to be able to separate CO2 from N2, CO2 and O2 mixture. However, the permeation of CO2 through the metal-carbonate membrane requires the presence of oxygen and the membrane suffers from a stability issue due to metal oxidation and metal-carbonate interaction. These problems have been addressed by replacing the metal phase with a mixed electronic-ionic conducting metal oxide phase.
Recently, the inventors have reported that a dual-phase membrane consisting of a molten carbonate (LiCO2/Na2CO3/K2CO3) entrapped in a porous perovskite-type La—Sr—Co—FeO3 ceramic support is perm-selective to CO2 (with CO2/N2 selectivity well above 225) with CO2 permeance of above 1.0×10−8 mol/m2·s·Pa at temperatures above 500° C. These dual-phase membranes had a thickness larger than 300 μm to 3 mm and were prepared with a disc-like configuration. However, these dual-phase membranes in a disc-like configuration having larger thicknesses were found not to have any practical applications.
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